Bullets are well known in the art. A bullet is the projectile that is discharged from the barrel of a gun. The bullet is driven into the rifled portion of a barrel by high pressure gas generated from the burning of a propellant (gun powder), which is typically ignited by a primer, as is well known in the art. The term “bullet” is often used to incorrectly refer to a complete ammunition cartridge. A cartridge, as properly used, includes a case (or casing) that holds the propellant in an interior chamber. Propellant is often referred to as an explosive, but it is not technically an explosive since, if ignited unconfined, it simply burns. The case will have a primer pocket that holds a primer which is used to ignite the propellant by flame going through the flash hole. There are two types of primers and primer pockets, Berdan and Boxer. The most common primer used in the U.S. is the Boxer primer. It allows for using a pre-fired case for reloading. The bullet is seated in the throat or open end of the case and held in place by friction, and perhaps crimping of the open end of the case.
As simple as shooting a bullet may sound, there is a large body of science regarding what is referred to as ballistics, which can be broken down into three main categories: internal ballistics, external ballistics, and terminal ballistics. Internal ballistics concerns itself with what happens during propellant burning in the barrel until the bullet is discharged from the barrel. External ballistics is the science regarding the flight of the bullet. Terminal ballistics is the study of how the bullet behaves when it strikes the target, including the transfer of kinetic energy of the bullet to the target.
In terminal ballistics, some bullets have been designed to mushroom (or expand) when contacting and/or traveling within the target, while some bullets are designed to resist such expansion. Hunting and defense bullets are typically designed to expand. One important factor in expansion is bullet speed at impact, i.e., its kinetic energy. Kinetic energy is related to bullet speed in accordance with the square of its speed. Thus, a bullet having half the speed of another bullet of the same mass has one quarter of its kinetic energy.
There are two issues regarding speed. The industry uses the term velocity in this regard, rather than the term speed. Velocity is a vector quantity needing both magnitude and direction. Speed is not a vector quantity, and thus only includes magnitude. Throughout this application, the term “speed” will be used contrary to the industry practice. Many cartridges are designed to provide a low speed bullet, while many are designed to provide a high speed bullet. Pistol bullets tend to be low speed. Centerfire type rifle bullets tend to be high speed, although slower than normal speed ammunition has recently entered the market. In one example, high speed bullets are designed to travel their entire course at supersonic speed. However, during long range shooting, many high speed bullets will have a decrease in speed, and subsequently change from supersonic speed to subsonic speed. Some writers have implicated the transition from supersonic to subsonic as problematic for both accuracy and precision, hence a trend to use bullets having subsonic speeds throughout their course. In general, subsonic bullets also have less initial energy associated with their internal ballistics, and thus exhibit less recoil to the shooter. Additionally, shooting bullets at subsonic speed should result in less barrel wear, extending the life of the firearm. Bullet speed is determined by many factors, including primer, amount and type of powder, rifling twist rate, bullet weight, and barrel length.
Today's rifle bullets, particularly hunting and defense bullets, have been designed for expansion in the target at supersonic speed. Depending on temperature, humidity and barometric pressure, the speed of sound in air is about 1,125 feet/second, which for purposes of this application will be the speed of sound. Below this speed is subsonic and above is supersonic.
Pistol bullets designed for expansion are typically of a hollow point construction to obtain expansion. Rifle bullets that are supersonic upon exit from the barrel can be of either a hollow point construction, often used for match ammunition, or can have a pointed tip, such as provided by a polymeric tip insert at its leading end to help initiate expansion of the bullet. Once expansion is initiated, the bullet will continue its expansion, including expansion of the core. A modern rifle bullet is typically a jacketed bullet with a soft dense metallic core, typically a lead alloy core, while the jacket is of a copper alloy. It is desirable for most such bullets to retain as much of their original mass as practical during target penetration. This can be accomplished by, e.g., bonding the core to the jacket and/or mechanical means, such as an inwardly extending rib on the jacket extending into a groove in the core.
A hollow point bullet, often simply referred to as a hollow point, has a central cavity or opening at the nose of the bullet which facilitates the hollow forward end flaring outward upon impact to create a broader profile. This is more disruptive of tissue, providing increased effectiveness. However, hollow point bullets have certain disadvantages. The amount by which the bullet expands is important, with under-expansion and over-expansion limiting effectiveness. If the bullet does not adequately expand, then it has less disruptive effect, leading to reduced stopping power and possible over penetration of the target, endangering bystanders, or at least limiting effectiveness by failing to deliver some of the bullet's energy to the target as impact. An over-expanded round delivers more impact to the target because of higher deceleration, but has limited penetration. This can also diminish the intended effectiveness against targets.
Moreover, if a criminal attacker is wearing heavy clothing, such as denim or leather, the clothing material may clog the hollow point, preventing or substantially reducing expansion, and thus reducing impact (energy transfer) and effectiveness. Another problem with conventional hollow point bullets is that an off-axis impact on hard material, such as sheet metal or glass, can tend to cause the hollow point's leading edge to bend, closing it up and preventing or impeding expansion upon eventual impact with the ultimate target.
Some bullets have hollow points formed in the bullet body (typically formed of a lead alloy with a copper alloy jacket) with the hollow cavity filled with an element of a different material. Rifle bullets may have a hollow cavity filled with a pointed tip element to provide an aerodynamic profile, and which facilitates expansion upon impact at high speed. Certain pistol bullets employ a round plastic ball that partially fills a bullet's cavity, preventing clogging with clothing material and facilitating expansion. While these variations provide some benefits, there remains a need to generate more effective and controlled expansion of bullets. A particular concern is that, while high-speed rifle bullets readily expand upon impact, lower speed rounds expand less reliably. What works to effect expansion of a high speed bullet, may not work as intended with a slow speed bullet and vice versa. Expansion is a process, not an event.
Achieving expansion of a non hollow point bullet at subsonic speeds has been a challenge to the prior art. The present invention overcomes this deficiency.